The present invention relates to an optical system for simulating on a beam of light the effects of traveling over a large distance and, more particularly, to such an optical system in which light exiting the system has the same direction, relative position, and intensity distribution which it would have after traveling a substantially greater distance.
Various types of optical equipment have been developed which utilize a beam of laser light (or a beam of incoherent light) as a reference over substantial distances. For example, a laser beam may be rotated in a selected horizontal or graded angle plane at a construction site and detected by appropriate survey detectors, as suggested by U.S. Pat. No. 4,062,634, issued Dec. 13, 1977, to Rando et al, and assigned to the assignee of the present invention. Such a laser beam projection arrangement may also be utilized with equipment which effects automatic control of grading machinery. Stationary beam projection devices are utilized in trenching operations and many other construction applications. With all such applications, it is common for the laser beam to be detected at substantial distances from the projection device, on the order of 1500 feet or more.
It will be appreciated that a part of evaluating a laser beam projection device or an incoherent optical beam projection device is the evaluation of the beam which it produces at typical operating distances from the projection device. It is desirable to determine the direction, divergence, intensity distribution, and cross-sectional shape of the beam at working distances. Optical components, such as lenses, which are used in optical equipment that works over long distances, often have small imperfections, which cause small distortions in the optical beam that only become apparent at long distances. In order to avoid unnecessary and costly rejections of imperfect optical components, it is sometimes desirable to observe directly what effect those components will have when the optical equipment is used at long distances. This permits rejection criteria to be related to the actual condition in which the components are used.
Heretofore, it has been necessary to test laser beam projection devices, and other optical systems which operate over substantial distances, by actual tests made at normal working distances. This is both inconvenient and a source of possible measurement error. If a laser projection device is tested outdoors, the beam produced will typically be subjected to refraction by thermal variations in the air over the beam path. Air movement will continuously alter the refraction produced in this manner, making accurate testing difficult. Additionally, if the test requires that ambient light be eliminated or minimized, it may be necessary to perform the test at night.
It will be appreciated that it would be much preferred to perform testing under the controlled conditions afforded by a laboratory, but that most laboratories are too small in size to permit the projection of light over substantial distances. Accordingly, it is seen that there is a need for an optical system which permits the simulation of substantial distances within confined space limitations.